The present invention relates to a decomposition processing apparatus for PCB which heats and decomposes liquid PCB (polychlorinated biphenyl). More particularly, the present invention relates to a decomposition processing apparatus for subjecting liquid PCB to thermolysis by utilizing a heating device such as a blast furnace.
Since liquid PCB (which will be simply referred to as xe2x80x9cPCBxe2x80x9d hereinafter) has an excellent electrical insulating characteristics, it has been widely utilized as an electrical insulator in the past. However, even though PCB is subjected to disposal after use, it is not decomposed and pollutes air, water, soil and others. Further, it enters human bodies through foods, and it is also hard to be decomposed in human bodies. It takes time for PCB to be excreted and it is hence accumulated in the human bodies. Therefore, processing for defusing the existing PCB is demanded.
In order to decompose and defuse PCB, there has been generally adopted a technique for performing thermolysis by using a heating device. Its conditions are as shown in, for example, Table 1. As apparent from this table, a heating temperature must be increased and a staying time of PCB in the heating device must be also prolonged in order to improve a decomposition ratio of PCB.
However, even if a temperature for heating PCB is tried to be increased, there is a limit of heat resistance of the heating device or a quantity of the energy consumption and actually a temperature of approximately 1500xc2x0 C. is an upper limit in actual fact. Thus, in order to further improve the decomposition ratio of PCB, it is desired that the heating device is maintained at a temperature as high as possible and the staying time of PCB in the heating device is prolonged.
However, when a vertical furnace and the like is utilized to heat PCB in particular, even if PCB is dropped from the top of the furnace, it immediately reaches a lower part of the furnace, and the staying time becomes, e.g., not more than 0.5 second, thereby making it difficult to increase the decomposition ratio of PCB.
Thus, it is an object of the present invention to provide a decomposition processing apparatus for PCB which can prolong the staying time of PCB even in a vertical furnace and the like.
To achieve this aim, according the present invention, there is provided a PCB decomposition processing apparatus for subjecting PCB to thermolysis, the apparatus comprising: heating means; supplying means for supplying PCB in a heating atmosphere obtained by the heating means; and staying means which consists of a porous body having an affinity to PCB and heating resistance in the heating atmosphere, is arranged in the heating atmosphere to hold PCB supplied from the supplying means and temporarily causes PCB to stay in the heating atmosphere.
Since the staying means has an affinity to PCB, PCB is held by the staying means without being dripped off in the middle of processing. Therefore, the staying time in the heating space can be prolonged. Further, since PCB is held in the porous body, a contact area between PCB and heating air can be increased as compared with the case where PCB is retained in a container or flows in a groove-like channel as it is. Thus, since a contact area between PCB and oxygen can be increased and heat of the heating atmosphere can be efficiently supplied to PCB, the decomposition reaction of PCB can be facilitated. For these reasons, the decomposition ratio of PCB can be increased.
Further, it is preferable that a plurality of staying means are arranged in the vertical direction and guiding means is provided between the respective staying means, which retains PCB dropped from the staying means on the upper side in the heating atmosphere while guiding it to the staying means on the lower side. In this case, since PCB can be held by a plurality of the staying means in sequence by the guiding means, PCB can stay in the heating atmosphere for a long time. Also, PCB can be caused to stay in the heating atmosphere when guided by the guiding means.
Furthermore, it is preferable that the staying means is horizontally set and drops from the central part PCB supplied from the upper part, the guiding means is horizontally set and drops from the periphery of the guiding means PCB supplied from the upper part, and the staying means and the guiding means are arranged in the vertical direction in sequence. In this case, PCB supplied from the upper part of the decomposition processing apparatus is collected to the central part and caused to drop by the staying means. The dropped PCB is received by the guiding means arranged immediately below the staying means and caused to drop from the periphery. Moreover, the dropped PCB is received by another staying means arranged immediately below the guiding means, and alternate reception by the staying means and the guiding means is carried out for at least one time. As a result, PCB is also moved in the horizontal direction in addition to the dropping movement, the staying time of PCB in the heating space can be prolonged.
In addition, it is preferable that the staying means and the guiding means are platy have a dropping portion which protrudes downward being provided on each lower surface thereof and the dropping portions of the staying means and the guiding means which are adjacent to each other in the vertical direction are staggered in the horizontal direction and set.
For example, the dropping portion of the staying means is positioned at the center of the lower surface of the staying means, and the dropping portion of the guiding means is positioned on the periphery of the lower surface of the guiding means. Since the positions of the staying means and the guiding means to which PCB is dropped and the positions at which PCB is dropped from the staying means and the guiding means deviate from each other in the horizontal direction, the time that PCB is held in the staying means and the guiding means is prolonged, and the staying time in the heating atmosphere can be extended.
Alternatively, the staying means and the guiding means may be platy, and they are slightly inclined from the horizontal state and alternately arranged in the vertical direction by alternately changing the inclination directions. Further, of the staying means and the guiding means which are adjacent to each other in the vertical direction, a part which is slightly lower than an uppermost part of the lower means may be positioned directly below a lowermost part of the upper means. In this case, PCB supplied to the staying means or guiding means on the uppermost stage is held in that means and temporarily stays. Thereafter, PCB drops from the lowermost part of that means. PCB falls on the part which is slightly lower than the uppermost part of the next means, and it stays and drops from the lowermost part while moving in the horizontal direction by that means. By repeating this process, PCB is subjected to thermolysis before dropping from the lowermost part of the staying means or the guiding means at the lowermost stage. Thus, since PCB is held while moving in the horizontal direction, the staying time in the heating space can be prolonged and PCB can be decomposed at a high ratio.
In particular, when the guiding means is a plate for dropping PCB from its periphery, since the distance for horizontal movement can be set maximum, the staying time can be prolonged. Further, when the guiding means is a perforated plate having at least one through hole for passing PCB and the heating atmosphere, since the heating atmosphere can pass through the guiding means, PCB can be more actively brought into contact with air, and heating of PCB can be attained. Therefore, thermolysis of PCB can be facilitated.
On the other hand, the staying means may be platy, and a plurality of the staying means may be arranged in the vertical direction. A dropping portion which protrudes downward may be provided on the lower surface of each staying means, and the dropping portions of the staying means which are adjacent to each other in the vertical direction may be staggered in the horizontal direction. Furthermore, the lower staying means may be arranged directly below the dropping portion of the upper staying means. In this case, since PCB can be held by a plurality of the staying means in sequence, it can be retained in the heating atmosphere for a long time.
Here, when the staying means having the dropping portion positioned at the center of the lower surface of the staying means and the staying means having the dropping portion positioned on the periphery of the lower surface of the staying means are alternately arranged, PCB which has dropped from the central part of the staying means having the dropping portion at the center drops from the periphery in the staying means on the next stage, and it drops from the central part again in the next means. This process is repeated. Therefore, since PCB is held while moving in the horizontal direction, the staying time in the heating atmosphere can be prolonged, and PCB can be decomposed at a high ratio.
Alternatively, the staying means may be slightly inclined from the horizontal state, and arranged in the vertical direction by alternately changing the inclination directions. Moreover, the staying means which are adjacent to each other in the vertical direction can be arranged in such a manner that a part which is slightly lower than an uppermost part of the lower staying means can be positioned directly below a lowermost part of the upper staying means. In this case, PCB which has been supplied to the staying means on the uppermost stage is held in that staying means and temporarily stayed, and then drops from the lowermost part of that means. PCB which has dropped now drops to the part which is slightly lower than the uppermost part of the staying means on the next stage, and is held in that staying means. After temporarily staying, PCB drops from the lowermost part of that means. By repeating this process, PCB is subjected to thermolysis till it drops from the lowermost part of the staying means on the lowermost stage. Since this process can also cause horizontal movement of PCB as well as dropping action, the staying time in the heating space can be prolonged, and PCB can be decomposed at a high ratio.
In addition, it is preferable that the staying means is accumulation type porous ceramics. In this case, the staying means having the porosity according to the dimensions of the staying means or a quantity of PCB to be processed can be arbitrarily molded. Here, the accumulation type porous ceramics is obtained by accumulating lines of ceramics extruded from a nozzle and forming a porous body with air holes generated between these lines.
This staying means may be ceramic noodles obtained by circularly winding and accumulating filate ceramics (for example, brand name: Actothermic manufactured by Kobe Steel, Ltd). The ceramic noodle has a such a shape as that many coil springs overlap and has the high thermal shock performance. In addition, the thermal shock performance of the ceramic noodle can be improved as compared with a honeycomb compact consisting of the same material.
When the staying means is made of the ceramic noodles, it is possible to obtain the staying means having porosities which differ depending on a filament diameter, a winding diameter or a difference in accumulation pattern. For example, when the filament diameter is changed to any of 1.0, 1.5, 2.0 mm and the like and the accumulation pattern is changed, the porosity can be adjusted to 40 to 80%. Therefore, the staying means having the porosity according to a quantity of PCB to be processed can be arbitrarily molded.
As the staying means, one obtained by accumulating filament ceramics in the lattice form may be used. In this case, the staying means having the different porosity can be likewise obtained in accordance with a difference in accumulation pattern such as a filament diameter, an interval between lines or an angle of overlap. Therefore, the staying means having the porosity according to a quantity of PCB to be processed can be selected.
Here, as the accumulation type porous ceramics, one made of mullite or alumina can be used. Since a fusing point of each of mullite and alumina is not less than 1800xc2x0 C. and a softening temperature of the same exceeds 1450xc2x0 C., the heat resistance in the heating atmosphere can be provided. Mullite is expressed by a composition formula 3Al2O3.2SiO2, and its composition ratios are Al2O3:76.6 wt % and SiO2:23.1 wt %.
Further, the staying means may be a block body or a honeycomb structure consisting of a porous material. In such a case, since a contact area between PCB and heating air can be likewise increased, a contact area between PCB and oxygen can be increased and, at the same time, heat of the heating atmosphere can be efficiently supplied to PCB. Therefore, the decomposition reaction of PCB can be proceeded and the decomposition ratio can be increased.
On the other hand, in this PCB decomposition processing apparatus, it is preferable that the heating means is a combustion portion of a blast furnace and the supplying means and the staying means are installed in the blast furnace. Therefore, since the thermal energy of the blast furnace can be directly used for thermolysis of PCB, the lost thermal energy is small and the decomposition efficiency can be increased. Also, PCB can be heated at a temperature of 1000 to 1450xc2x0 C. which is preferable as a heating temperature for increasing the decomposition ratio of PCB to not less than 99.9999%.
Further, it is preferable that a temperature for heating PCB is 1000 to 1450xc2x0 C. and a time for heating PCB is 1.0 to 3.5 seconds. If the temperature and the time fall within these ranges, the decomposition ratio of PCB can be set to not less than 99.9999%. In order to increase the decomposition ratio of PCB to not less than 99.9999%, if the heating temperature is, e.g., 1450xc2x0 C., the staying time of 1.0 second can suffice. Furthermore, if the staying time is, e.g., 3.5 seconds, the heating temperature of 1000xc2x0 C. can suffice.
Moreover, the heating temperature required for increasing the decomposition ratio of PCB to not less than 99.9999% is preferably 1000 to 1450xc2x0 C. and, more preferably, it is 1200 to 1400xc2x0 C. In order to increase the decomposition ratio to not less than 99.9999% with the heating temperature which is less than 1000xc2x0 C., the staying time must be prolonged so as to exceed, e.g., 3.5 seconds. As a result, the path of PCB becomes long and the size of the decomposition processing apparatus is increased, which is not preferable. Moreover, with the heating temperature exceeding 1450xc2x0 C., the staying means made of ceramics may be possibly deformed, which is not preferable.
In addition, as the staying time required for increasing the decomposition ratio of PCB to not less than 99.9999%, it is preferably 1.0 to 3.5 seconds and, more preferably, it is 2.0 to 3.5 seconds. In order to obtain the decomposition ratio which is not less than 99.9999% with the staying time less than 1.0 second, the heating temperature must be increased so as to exceed 1450xc2x0 C., which is not preferable. Additionally, the staying time exceeding 3.5 seconds extends the path of PCB and increases the size of the decomposition processing apparatus, which is not preferable.